WIKA TR25 (Ex i), Руководство по эксплуатации

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EN
14073045.06 10/2020 EN/DE/FR/ES
WIKA operating instructions model TR25 (Ex i) 26
8. Calculation examples for self-heating of the pipe body at
the sensor mounting point
In-line resistance thermometer model TR25 with built-in head-mounted transmitter
model T32.1S.
Power supply is, for example, via a model KFD2-STC4-EX1 repeater power supply
(WIKA article no. 2341268).
T
max
is obtained by adding the temperature of the medium and the self-heating. The
self-heating depends on the supplied power P
o
of the transmitter and the thermal
resistance R
th
.
The following formula is used for the calculation: T
max
= P
o
x R
th
+ T
M
T
max
= Surface temperature (max. temperature of the pipe body at the sensor mounting point)
P
o
= from transmitter data sheet
R
th
= thermal resistance [K/W]
T
M
= medium temperature
The precondition is an ambient temperature T
amb
of -20 ... +40 °C.
Thermal resistance for TR25 (R
th
) 60 K/W
Example
Medium temperature: T
M
= 150 °C
Supplied power: P
o
= 15.2 mW
Temperature class T3 (200 °C) must not be exceeded
Thermal resistance [R
th
in K/W] = 60 K/W
Self-heating: 0.0152 W x 60 K/W = 0.91 K
T
max
= T
M
+ self-heating: 150 °C + 0.91 °C = 150.91 °C
The result shows that, in this case, self-heating of the pipe body at the sensor mounting
point is negligible.
As safety margin for type-examined instruments (for T6 to T3), an additional 5 °C must be
subtracted from the 200 °C; hence 195 °C would be permissible. This means that in this
case temperature class T3 is not exceeded.
Additional information
Temperature class for T3 = 200 °C
Safety margin for type-tested instruments (T6 to T3)
1)
= 5 K
Safety factor for type-tested instruments (T1 to T2) 1) = 10 K
1) IEC/EN 60079-0: 2009 section 26.5.1
8. Calculation examples for self-heating of the pipe body at ...